I'm new here, and have a major question I need answered. I Listen to Pandora Internet Radio (pandora.com), and I've recently noticed that they switched formats. They used to stream 128kbps MP3s, (which were LAME encoded, according to the file header), but now they seem to be sending 64kbps AAC/MP4s. The file identifies itself as "ISO Media, MPEG v4 system, version 2", and it plays properly in mplayer and ffmpeg (ffplay), as well as VLC and Windows Media Player through a Nero Decoder.

In all of those, it sounds great - I can't tell the MP4 apart from the MP3 for the same song. Playing to Quicktime yields the opposite: it sounds horrible, as if it was a 64kbps MP3.

Usually, I can't tell the difference between 128kbps MP3s and higher quality, but this has be baffled. I can't figure out if the MP3 or AAC/MP4 is better. A couple of friends have tried, and none can tell the difference either.

So, the question comes out: which is better: AAC/MP4 or MP3, or are they the same?

He-AAC is a technology that makes AAC sound much more convincing at low bitrates, and I feel that it does a pretty nice job. However, it's not supported by all decoders - this would explain why the playback suffers in QuickTime, it doesn't support He-AAC.

The "which one is better question" is debatable, with LOTS of factors that need to be taken into account. It is entirely possible that the two streams are just as transparent, but there would be no way to know for sure without performing some ABX testing.

If you better acquaint yourself with the HA wiki you will find all the tools you need to make an informed decision for yourself.

In all of those, it sounds great - I can't tell the MP4 apart from the MP3 for the same song. Playing to Quicktime yields the opposite: it sounds horrible, as if it was a 64kbps MP3.

That's because 64 kbps AAC file is HE-AAC, which is normal AAC + SBR information used to reproduce high frequencies. However, QuickTime (at least on Windows, don't know about Mac) seems to ignore SBR information, which means that part of the sound information is actually missing resulting in lower quality.

I don't know why Apple still does not have proper HE-AAC support in QuickTime, given the fact that almost all other decoders/player have proper HE-AAC support.

QUOTE

Usually, I can't tell the difference between 128kbps MP3s and higher quality, but this has be baffled. I can't figure out if the MP3 or AAC/MP4 is better. A couple of friends have tried, and none can tell the difference either.

So, the question comes out: which is better: AAC/MP4 or MP3, or are they the same?

In my opinion, 128 kbps MP3 file (lame-encoded) sounds better than 64 kbps AAC. But if you can't tell the difference between the two (ABX testing may help in determining whether this is the case or not), I would suggest using whatever is more convenient for you.

Thank you for the replies so far. I will most definitely conduct some tests, double-blind if I can. I just need to collect some more AAC audio files first.

However, I do have a question: is there a way to identify more information about the file? I've run it through my Windows tools (VLC, Windows Media Player) and Linux (ffmpeg, mplayer) and found out this:Codec: mp4aChannels 2:Sample rate: 44100HzBits per sample: 16AAC extension: SBR

It also reports (in VLC, on the Advanced information tab) the bitrate to be 1411 kb/s, but then on the Statistics tab it shows 64 kb/s. Is there any more information I could extract from these files?

Again, thank you for your replies. Your comments about HE-AAC are right on the money. Based on the stream information, it's HE-AAC v1.

This means that the compressed file is 64 kb/s but it decodes to 1411 kb/s.

I'm sorry, I don't understand. Does that mean that the 64kbps stream contains 1411 kb/s worth of information? That seems like an uncompressed WAV or lossless codec. If it makes a difference, VLC properly reports a 128kb/s MP3 as 128 kb/s on both screens.

This means that the compressed file is 64 kb/s but it decodes to 1411 kb/s.

I'm sorry, I don't understand. Does that mean that the 64kbps stream contains 1411 kb/s worth of information? That seems like an uncompressed WAV or lossless codec. If it makes a difference, VLC properly reports a 128kb/s MP3 as 128 kb/s on both screens.

-gotPSP

I was merely pointing out that 2 channels/16 bits per channel/44100 samples per second is 1411 kb/s. Why this is being reported rather than 64 kb/s I don't know.